This invention pertains to pumps which are able to operate totally or partly submersed in the pumped medium, such as vortex-flow type pumps, and in particular to a novel housing for such vortex-flow type pumps.
Commonly, the pumped medium, to which the pumps are applied, contains some considerable amount of solid bodies. Waste water, and water found on construction sites, are typical of the pumped media which have solid bodies therein, and for such applications, the so-called vortex-flow type pump provides certain advantages over the conventional centrifugal pump, especially with respect to small dimensions thereof.
A vortex-flow type pump is characterized by the fact that the impeller is axially displaced in the pump housing as compared with a conventional centrifugal pump. This means that a wide, free throughlet is obtained, and thus the risk for clogging is often diminished. Consequently, it is then often possible to use smaller pumps for pumping heavily polluted liquids, and thus the costs can be reduced. Too, the fact that a vortex impeller is simpler to manufacture than a centrifugal impeller further decreases the costs.
The vortex-flow type pump, however, has certain disadvantages. Its efficiency is often lower as compared with a conventional centrifugal pump. The head often becomes lower even at small volume flows and, in addition, the power demand thereof rises rapidly at increasing volume flow.
In the conventional vortex-flow type pump, liquid is sucked in axially, through an inlet and is thrown towards the circumference of the housing by the impeller vanes, and is finally pushed out through the outlet. The housing area between the bottom of the housing and the impeller vanes has a prescribed minimum dimension, which is dictated By cognizant authorities, when waste water is pumped. This is to insure that solid bodies, up to a certain dimension, shall be able to pass through the pump without being blocked. The disadvantage caused by the vanes-to-housing bottom area is that eddies occur which bring back a part of the of the liquid to the center, and in addition check the rotation of the impeller and increase the risks for cavitation and vibration. The Swedish Patent No. 462 869 shows a pump in which such problems are alleged to be solved by providing the impeller vanes with deflection means toward preventing the liquid from flowing back to the center. A problem with this approach, however, is that the risks for clogging increase.
As noted, a disadvantage of the vortex-flow type pump is the strong increase of power demand at increasing volume flow. A prior art device which addressed this problem is shown in the Swedish Patent No. 374 415 in which the pump housing is provided with elastic parts which choke the throughlet at certain pressure conditions.
The purpose of this invention is to disclose a housing for a vortex-flow type pump having an increased efficiency and an increase in the possible head thereof, especially at small volume flows.